Many natural sources of hydrocarbons contain high percentages of non-hydrocarbon components, such as nitrogen, carbon dioxide, helium and hydrogen sulphide. Also however, techniques for the production of synthetic natural gas typically result in methane contaminated with hydrogen and carbon monoxide. For most applications to which the hydrocarbons will ultimately be put, it is desirable to remove these non-hydrocarbon contaminants.
Further, for simple hydrates, carbon dioxide forms a structure I hydrate, whilst nitrogen preferentially forms a structure II hydrate. However, the structure of the hydrate formed by a mixture of nitrogen and carbon dioxide may be either structure I or structure II, depending on the composition of the mixture and the pressure at which the hydrate was formed.
Despite this complexity, the separation of compounds based on their differing tendency to form hydrates has been proposed. For example, in U.S. Pat. No. 5,434,330, Hnatow and Happel describe a process and apparatus for controlling the formation and decomposition of gas hydrates to improve separation rates. The method described therein involves contacting a mixture of gases with an pre-cooled aqueous medium to form a suspension of solid hydrate therein. The pre-cooled aqueous medium contains high concentrations of methanol, intended to enable the aqueous medium to be cooled to lower temperatures without freezing.
The methanol is also used as a separating agent based on the differing solubilities of the gases of the mixture therein.
However, the process described in U.S. Pat. No. 5,434,330 requires elevated pressures, and low temperatures to produce the hydrate, adding considerably to the expense of the process.
It is an object of this invention to provide an alternative method for the separation of non-hydrocarbon gases from hydrocarbon gases.
The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.
Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.